1. Field of the Invention
This invention relates generally to earth bits having rotatable cones.
2. Description of the Related Art
An earth bit is commonly used to bore holes through earthen annulus. Such holes may be bored for many different reasons, such as drilling for oil, minerals and water. One type of earth bit used for drilling is a rotary earth bit, and several examples are disclosed in U.S. Pat. Nos. 3,550,972, 3,847,235, 4,136,748, and 4,427,307. A rotary earth bit generally includes three earth bit cones rotatably mounted to corresponding lugs. The lugs form a portion of an earth bit body and, as the earth bit body rotates, the cones rotate in response to contacting the earthen annulus.
The rotation of a cone with respect to its corresponding lug is often facilitated by using roller and ball bearings. The ball bearings also operate to retain the cone to the lug, but the roller bearings generally do not. The ball bearings retain the cone to the lug because they extend into opposing grooves formed through them. The opposing grooves are generally machined through the lug and cone, which requires accurate measurements. Inaccuracies in these measurements can cause the cone to be unbalanced so it improperly rotates relative to the lug. When the cone improperly rotates relative to the lug, it wobbles and causes the earth bit to undesirably vibrate.